The present invention disclosed herein relates to a secondary battery, a battery module, and a battery pack, which have improved safety.
Secondary batteries, which are rechargeable, are widely used as an energy source of wireless mobile devices. In addition, secondary batteries are regarded with much interest as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are expected to reduce a it pollution caused by typical gasoline and diesel vehicles using fossil fuels.
One to four battery cells are used in a small mobile device, whereas a medium-to-large battery module including a number of battery cells electrically connected to one another is used in a medium-to-large device such as an automobile requiring high power and high capacity. To optimally reduce the size and weight of medium-to-large battery modules, prismatic-type batteries and pouch-type batteries, which have high integration and small weight-to-capacity ratio, are widely used as battery cells in medium-to-large battery modules.
Particularly, since pouch-type batteries including an exterior part such as an aluminum laminate sheet are light weight, economically manufactured, and easily transformed, they attract a lot of attention.
Medium-to-large battery modules include a number of battery cells electrically connected to one another in series to provide power and capacity needed by a certain apparatus or device, and have a stable structure against external force.
Battery cells constituting a medium-to-large battery module are rechargeable secondary batteries. Of these, lithium secondary batteries have high energy density, high voltage, long service life, and low self discharge rate.
One of main efforts for developing secondary batteries is to improve safety. Particularly, since secondary batteries, used in a medium-to-large battery pack as a power source of electric vehicles and hybrid vehicles, include a number of highly integrated high energy battery cells, and contain organic electrolyte having a low ignition point, it is important to ensure their safety.